/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package com.aliyun.odps.lot.common;

import apsara.odps.lot.ExpressionProtos;

/**
 * 值表达式. null reference == NULL constant.
 */
public abstract class ScalarExpression {

  public abstract ExpressionProtos.ScalarExpression toProtoBuf();

  public static ExpressionProtos.ScalarExpression genNull() {
    apsara.odps.ExpressionProtos.Null.Builder n = apsara.odps.ExpressionProtos.Null.newBuilder();
    ExpressionProtos.ScalarExpression.Builder
        builder =
        ExpressionProtos.ScalarExpression.newBuilder();
    builder.setNull(n.build());
    return builder.build();
  }
}
